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Full text of "The Cambridge Natural History"

ii                            LEMURS   AND   THEIR   YOUNG                          19
teat would of course be absolutely incomparable with a mammary
pouch, because in that case the wall of the teat itself would be
the pouch.
Mammals belonging to quite different Orders show traces
more or less marked of a mars opium. In young Dogs the teats
are borne upon an area where the skin is thinner, the covering
of hair less dense than elsewhere—all points of resemblance to
the inside of the pouch of a Marsupial; in addition to this
there are traces of the sphincter marsupii muscle. In other
Carnivora there are similar vestiges. In Lemur catta a more
complete rudiment of a marsupial pouch is to be met with. In
this Lemur the teats are both inguinal and pectoral; the skin
in these regions is thin and but slightly hairy, and extends
forwards as two bands of the same thinness and smoothness on
each side of the densely hairy skin covering the sternum. This
area is sharply separated from the rest of the integument by a
fold which runs parallel to the longitudinal axis of the body,
and can be comparable with nothing save the rudiment of the
marsupial fold.
One is tempted to wonder how far the habit which certain
Lemurs have of carrying their young across the abdomen with
bhe tail wrapped round the body of the mother is a reminiscence
Df a marsupial pouch.
Skeleton.
The skeleton of the Mammalia consists almost solely of the
indoskeleton. It is only among the Edentata that an exo-
skeleton of bony plates in the skin is met with. As in other
Vertebrates, the skeleton is divisible into an axial portion,
ihe skull and vertebral column, and an appendicular skeleton,
ihat of the limbs. The bones of mammals are well ossified,
ind in the adult there are but few and small tracts of cartilage
left.
Vertebral Column.—The vertebral column of the mammals,
ike that of the higher Vertebrata, consists of a - number of
separate and fully-ossified vertebrae.
The constitution of a vertebra upon which all the usual
>rocesses are marked is as follows ;—There is first of all the
>ody or centrum of the vertebra, a massive piece of bone shaped
ike a disc or a cylinder. The centra of contiguous vertebrae